Recycling of agro-industrial sludge through vermitechnology

Abstract

This work illustrates the feasibility of vermitechnology to stabilize sludge from an agro-industry. To achieve the goal, industrial sludge (IS) was mixed with three different bulky agents, i.e. cow dung (CD), biogas plant slurry (BGS) and wheat straw (WS), in different ratios to produce nine different feed mixtures for earthworm Eisenia fetida. Vermicomposting bedding material was analyzed for its different physic-chemical parameters after 15 weeks of experimentations. In all waste mixtures, a decrease in pH, organic C and C:N ratio, but increase in total N, available P, exchangeable K, exchangeable Ca and trace elements (Mg, Fe and Zn) was recorded. IS (40%) + CD (60%) and IS (40%) + BGS (60%) vermibeds showed the highest mineralization rate and earthworm growth patterns during vermicomposting process. Vermicompost contains (dry weight basis) a considerable range of plant available forms of P (17.5–28.9 g kg −1), K (13.8–21.4 g kg −1), Ca (41.1–63.4 g kg −1), Mg (262.4–348.3 mg kg −1), Fe (559.8–513.0 mg kg −1) and Zn (363.1–253.6 mg kg −1). Earthworm growth parameters, i.e. biomass gain, total cocoon production, individual growth rate (mg wt. worm −1 day −1), natality rate, total fecundity were optimum in bedding containing 20–40% industrial sludge. C:N ratio of worm-processed material was within the agronomic acceptable or favorable limit (<15–20). The results clearly suggested that vermitechnology can be a potential technology to convert industrial sludges into vermifertilizer for sustainable land restoration practices.